Synthetic grass with resilient granular top surface layer

ABSTRACT

A synthetic grass assembly for installation on a supporting soil substrate includes a pile fabric with a flexible sheet backing and rows of upstanding synthetic ribbons representing grass blades, extending upwardly from an upper surface of the backing. An infill layer of two distinct graded courses of particulate material is disposed interstitially between the upstanding ribbons upon the upper surface of the backing and of a depth less than the length of the ribbons. A bottom course of intermixed hard sand and resilient rubber granules with substantially identical particle size distribution characteristics is installed upon the backing and a top course exclusively of resilient rubber granules is placed upon the bottom course.

This application is a divisional of application Ser. No. 09/598,149,filed on Jun. 21, 2000, now U.S. Pat. No. 6,551,689 and for whichpriority is claimed under 35 U.S.C. §120. Application Ser. No.09/598,149 is a CIP of PCT International Application No. PCT/CA99/00704filed on Aug. 3, 1999 under 35 U.S.C. §120. This application also claimspriority of application Ser. No. 2,247,484 filed in Canada on Sep. 21,1998 under 35 U.S.C. §119. The entire contents of each of theabove-identified applications are hereby incorporated by reference.

TECHNICAL FIELD

The invention is directed to a synthetic grass with grass-like ribbonsforming a lattice enmeshing a particulate infill having a bottom layerof equally sized sand and rubber granules, and a top layer of rubbergranules only.

BACKGROUND OF THE ART

Maintenance of natural grass turf on athletic playing or landscapedareas is expensive, natural grass does not grow well within shadedenclosed stadiums and continuous heavy traffic wears out areas in thenatural turf surface. Natural turf surfaces deteriorate under heavy useand exposed soil creates an undesirable accumulation of water and mud.Synthetic grasses therefore have been developed in order to reduce theexpenses of maintaining heavily used athletic playing areas, to renderplaying surfaces more uniform, and increase the durability of the grasssurface, especially where professional sports are involved.

Synthetic grass is installed with a carpet-like pile fabric having aflexible backing laid on a well drained compacted substrate, such ascrushed stone or other stabilized base material. The pile fabric hasrows of upstanding synthetic ribbons representing grass blades extendingupwardly from the top surface of the backing.

Of particular interest to the present invention are the variousformulations for granular resilient fill that are placed between theupstanding ribbons on the upper surface of the backing to simulate thepresence of soil. Most prior art systems involve some use of hardparticles such as sand or crushed slag particles, together withresilient particles such as crumb rubber particles or foam backing toprovide resilience. The optimal choice of particle sizes, particleshape, particle composition and installation in multiple layers orcourses is a feature of the present invention.

U.S. Pat. No. 4,337,283 to Haas, Jr. discloses a homogeneous infillmixture to imitate soil that is made of fine hard sand particles mixedwith 25% to 95% by volume resilient particles to provide an improvedresilient and less abrasive infill. Such resilient granular material mayinclude mixtures of granulated rubber particles, cork polymer beads,foam rubber particles, vermiculite, and the like.

U.S. Pat. No. 4,396,653 to Tomarin discloses a non-homogeneous infillwith rubber particles forming a base layer and sand particles forming atop layer. The rubber particles provide inner resiliency to the surface.The sand layer is exposed and forms a stabilizing cover layer for theunderlying rubber particle layer.

A number of disadvantages result from the use of a uniformly mixedgranular infill as in the Haas system where hard sand particles andresilient rubber particles are mixed and blended in a uniform proportionthroughout the depth of the infill. Synthetic grass infill, for example,may comprise a mixture of 60% by weight of sand and 40% granulatedrubber particles uniformly mixed and deposited between the upstandingsynthetic grass ribbons to a depth of 1 to 3 inches.

A high percentage of sand is preferred to minimize the cost of suchsystems, since rubber particles are relatively expensive compared tosand. The sand particles also provide an improved degree of drainagethat is needed where the synthetic grass surface is not in an enclosedstadium for example. Rubber particles tend to impede the free flow ofwater, whereas the capillary action of the sand particles draws surfacemoisture downwardly due to the differences in surface tensioncharacteristics between rubber and silica sand.

However, in both the Haas and Tomarin systems, abrasive hard sandparticles present in the top surface layer of infill causes problemswhere such as games of football, rugby, soccer, field hockey, baseballare played since players repeatedly fall down or are knocked down on theplaying surface. In such applications, there is a need to protectplayers from skin abrasion caused by the hard sand in the granularinfill and from sand spraying into the players eyes, ears and mouth.

The conventional infill is a mixture of sand and rubber particles. Therubber particles are compressed and released when a ball hits thesurface or an athlete steps on the surface. In the case of conventionalsoil, the soil and humus particles provide some natural resilience butthe rebound is more gradual due to moisture, small particle size andrelatively low natural resilience. In the case of synthetic infills, theparticles are relatively dry and do not bond together. The rubberparticles have a spring-like rapid resilient rebound that tends to hurladjacent sand particles and rubber upwardly under force.

The synthetic infill is continuously subjected to water flow and impactforces that tend to dislodge or segregate the particles, such as fromrainfall, flooding, the impact of bouncing balls, vibration and impactfrom the feet and bodies of players in contact with the top surface ofthe infill. A top layer with a high proportion of sand will result inspraying of sand particles when a ball or player impacts with the topsurface of the infill. When soccer balls roll on the infill surface, ifany sand particles are present at the top surface, sand particles arelifted by the rolling ball by the suction force of air flowing aroundthe spinning ball and by static electric attraction. As a result thesmaller sand particles on the top surface of the infill are lifted andsprayed in a “rooster tail” pattern behind the rolling ball. Over time,areas of continuous sand spray or ball impact will result in visiblesand on the playing surface. It is considered undesirable to have lightcolored sand visible in the synthetic grass surface and, especially whenclouds of sand are visible on such impacts. In addition, exposed sandgranules are highly abrasive to the skin when players fall or slide onthe top surface, and could irritate eyes, ears, nose and mouth whensprayed, inhaled or ingested.

A further disadvantage of conventional infills is that abrasive sandparticles remain on the top surface of the synthetic grass and playerson the surface who come in contact with the sand particles experienceskin abrasion. Over time, due to the dynamics of water, vibration andimpact, the smaller sand particles will tend to settle toward the bottomof the infill layer and larger more abrasive sand particles will rise tothe top surface. The small sand particles tumble downward in the voidsbetween larger particles under the influence of vibration, water andgravity. Smaller particles accumulate at the lower portion of a granularinfill layer and tend to compact together. The larger sand particlesremain at the top of the granular layer and large particles are highlyabrasive to human skin relative to the smaller particles.

As a result, over time the abrasive nature of the synthetic system isincreased and may result in particular areas of the playing surfacewhich experience heavy traffic being more abrasive than other areas.Conventionally used hard particles and resilient particles have angularsurfaces. It has been found however that angular particles tend tocompact together more than spherical or rounded particles since thefriction between sharp angular surfaces is greater. In addition, where awide range of particle sizes is used, the smaller particles fill in theinterstices between the larger particles and increase the degree ofcompaction.

When shredded rubber, or conventional ground rubber are used the rubberparticles have irregular surfaces often with fibrous protrusions thattrap air and hold water with surface tension. When the infill is rainedon or flooded, the air trapped by the lightweight rubber particlescauses the rubber particles to float. This is undesirable since therubber may wash down a drain with the surface water flow, and thefloating rubber separates from the heavier sand in the infill mixturethereby leading to particle segregation, sand compaction and loss of theresilience of the infill.

Where sand is used for construction purposes such as road building or inconcrete mixes, it is highly desirable to have a wide range of particlesizes specifically because a mix of small and large particles willresult in small particles filling of the interstices between largeparticles, increased inter-particle contact, superior compaction andtherefore a higher load bearing capacity. Where sand or granularaggregates are used in construction applications, vibratory compactorsare employed and moisture content is controlled to produce maximum soilcompaction and density.

However, where sand is used as a component of a resilient infill betweenthe interstices of synthetic grass, excessive compaction is highlyundesirable. A high degree of compaction of sand and contamination ofthe infill by airborne dirt and dust lead to unwanted changes in theresiliency of the infill over time as a result of use which may varyconsiderably over the synthetic grass surface from areas of high use toareas of low use. Uniform consistent resilience, elimination ofmaintenance and predictable performance of the infill are the goalsrather than high load bearing strength.

The conventional solution to the compaction and separation of infillparticles is to periodically brush the synthetic grass. Brushing servesto break up compacted material and remix the top surface restoring theoriginal composition of the infill mixture as much as possible. Brushingincreases the cost of maintenance, exposes synthetic ribbons tosignificant wear, and is at best a temporary solution since eventuallythe conventional infill compacts again and must be brushed regularly.

The proper choice of spacing between rows of grass ribbons has alsoproven to be problematic. Quite often the major complaint ofprofessional athletes is that cleats on shoes do not releaseconsistently from densely packed, matted, tightly woven or knittedsynthetic sport grass surfaces, causing knee and ankle injuries. Olderartificial grass surfaces were built much like indoor carpet surfaceswith very closely spaced upstanding fibers extending from a woven basewith resilient underlay. These fiber surfaces were designed to remainupstanding and avoid matting when stepped upon. Therefore to achievethis result, the fibers were spaced extremely close together. However,the cleats on athletic shoes often did not release properly especiallywhen the foot was spun on the surface, thereby resulting in knee andankle injuries.

On the other hand, where pure sand is used as a surface, in equestriansurfaces for example, the surface is relatively unstable and sandparticles displace easily. To stabilize such surfaces, U.S. Pat. No.4,819,933 to Armond (Fibresand Limited) provides a mixture of sand witha relatively small percentage by weight of straight synthetic fibersrandomly distributed and cross-linking in a loose displaceable network.The fibers serve to distribute concentrated loads, hold the sandtogether under the weight of horses hooves, athletic players' feet,wheeled vehicles or implements. U.S. Pat. No. 5,326,192 to Freed(Synthetic Industries, Inc.) also provides a method of improving theappearance and performance characteristics of a turf surface by workingdiscreet bunches of synthetic fibers into the soil surface.

Granular infill combined with upstanding grass-like synthetic ribbonsaddress the disadvantages of the above systems to a degree by providinga granular synthetic surface intermingled with the upstanding fibersextending from a fabric backing to better imitate a natural soil,embedded roots and grass. When the cleats on an athlete's shoe embed inthe granular infill, the loose particles shift and displace somewhatlike natural soil. At the same time the upstanding synthetic grassribbons enmesh with the loose particles and the cleats to reduce orprevent slipping. Without the synthetic ribbons, the loose particleswould be very difficult to run on much like a dry sand natural beachsurface whereas a dense mat of fibers would ensnare the cleatspreventing release and possibly causing personal injury.

Therefore the combined structure of upstanding ribbons and looseparticulate infill must be balanced or optimized to provide a desirableplaying surface. When the ribbons are densely packed together, thecleats cannot release properly, but when the ribbons are spaced too farapart, adequate traction and stability is not available. Due to the highcost of artificial grass installations, and risk of injury to highlyskilled and highly paid athletes, a predictable and reproducibleartificial grass performance is required.

Synthetic grass surfaces have also been constructed with infillsubstantially of rubber only. Rubber particles are relatively light, andshredded particles have fibrous surfaces that trap air bubbles. As aresult when flooded, the rubber particles of some conventionalinstallations have floated on the surface of water draining off thesynthetic grass surface. Rubber particles drain away or are displacedresulting in areas of the synthetic grass which have depleted infillthickness. A lack of uniform infill thickness and resilience across thesurface can result in injuries and liability for the owner of theathletic field.

Despite several different rubber and sand infill compositions and fiberstructures in the prior art, several significant disadvantages remain asnoted above.

It is an object of the present invention to provide an infill that willretain its properties throughout use without substantial segregation orcompaction of the infill and with a reduced requirement for periodicbrushing of the surface.

It is a further object of the invention to enhance the resilience andreduce the abrasive nature of conventional granular infills filling theinterstices of the synthetic grass ribbons while enabling the cleats ofathletic shoes to properly release without serious risk of injury.

It is a further object of the invention to eliminate the spraying ofsand particles and undesirable visible sand on the infill surface.

DISCLOSURE OF THE INVENTION

The invention provides a novel synthetic grass assembly for installationon a supporting soil substrate to provide a surface that combines thelook and feel of natural turf with the wear resistance of syntheticgrass. Although the description uses an athletic playing field as anexample, the invention is equally applicable to any area suitable forgrass cover such as high traffic landscaped areas, road and highwaymedians, indoor gardens or golf greens, and equestrian surfaces.

The grass assembly includes a pile fabric with a flexible sheet backingand rows of upstanding synthetic ribbons representing grass blades,extending upwardly from an upper surface of the backing. A unique infilllayer of two graded courses of particulate material is disposedinterstitially between the upstanding ribbons upon the upper surface ofthe backing and at a depth less than the length of the ribbons.

The ribbons are tufted through the water permeable fabric backing andhave intermittent longitudinal slits in a predetermined pattern. Duringinstallation of the infill, the ribbons are brushed lightly to returnthe ribbons to an upstanding position, from an initially matted positionthat results from the compression of ribbons due to rolling of thetufted fabric for shipping and storage after manufacture. The ribbonsmay be about one inch wide with several rows of slits across theirwidth. The light brushing tends to open a lower portion of the ribbonsand extend the slits open forming laterally linked strands disposed in alattice structure enmeshing the surrounding particulate infill. Once allthe infill is installed, the upper portion of the ribbons extendingabove the infill layer are brushed aggressively. The ribbons arelongitudinally split by the brushing action along the slits into severalindividual free-standing strands of a thinner width resembling grassblades.

The invention recognises that the granular infill is a dynamic system ofcontinuously moving hard and resilient particles of different sizes andwith different physical properties under the influence of impact andvibration from play activity, surface maintenance and weatherprecipitation. The invention accommodates such dynamic activity in anumber of ways.

The top surface is kept substantially sand free using a pure rubberparticle top course of relatively large particles, preferablysubstantially larger than those particles in the bottom layer. Anysmaller sand particles that migrate up to the top surface from thedisplacement action of cleats will then be able to percolate, throughthe voids between the larger top surface particles, downward back to thebottom course under the influence of water, vibration and gravity. Abottom course of sand and rubber mixed together is provided beneath thepure rubber top course for additional resilience, moisture drainage andas a ballast for stabilisation of the fabric backing.

The particle shapes are substantially spherical to reduce inter-particlecontact friction, improve drainage and prevent compaction. The sphericalshape reduces resistance to particle displacement and therefore reducesthe degree of compaction compared to conventional angular particles. Interms of the Krumbein sphericity standard, known to those skilled in theart, the particle shapes are broadly in the range of 0.5 to 0.99 butpreferably in the range between 0.6 and 0.9 being well rounded orsubstantially spherical.

The particle size distribution for hard sand and resilient rubberparticles in the bottom course are chosen to be substantially identicalto each other and preferably particle sizes are limited for sports orathletic playing surfaces to the range of 14-30 screen mesh standard. Toaccommodate other uses of the synthetic grass surfaces, the size ofparticles may range from 0.5 inches to 50 screen mesh standard. Largerparticles may be used for equestrian applications up to about 0.25inches but these large granules are too abrasive for contact with humanskin. Particles smaller than 50 screen mesh standard tend to create dustand may lead to undesirable compaction, reduced rate of waterpercolation and particle segregation. Naturally occurring soil particlesof this size range are classified as medium sand, coarse sand and finegravel sized particles.

By “substantially identical” size distribution it is meant that when thebottom infill layer is analysed through conventional soil laboratorysieve analysis, and graphically presented on a standard sieve analysissemi-logarithmic graph (y-axis showing 0-100 percent passing the sievesize or smaller by weight and x-axis showing sieve/particle sizelogarithmically) the line for hard particles and the line for resilientparticles are ideally superimposed on each other to a substantialextent. Therefore the hard and resilient particles have substantiallyequal particle sizes and the distribution of sizes is substantially thesame.

The standard sieve analysis graphs are by nature an imprecise “rough andready” measure, since natural soils vary considerably over the surfaceof a building site for example. The sieve analysis graphs generally donot show the largest 10% and the smallest 10% of particle sizes sincethese extremes are considered statistically insignificant due to thenatural variation in soil particle sizes. Therefore conventionally, onlythe middle 80% of particles are considered when examining soil particlesizes in a sieve analysis.

Applying this practice to the invention, numerically or scientificallydefined, where the particle sizes of 80% by weight of hard and resilientgranules in the bottom course are distributed in a range spanning anumerical difference of 40 screen mesh standard, the particle sizedistribution is considered substantially identical or very well sorted.Since the sand and rubber may be graded to any specification desired, itis preferred that the numerical difference be even less such as 20screen mesh standard to produce a more uniform infill. For example,completely spherical manufactured glass beads would have a numericaldifference approaching zero. However since sand is a naturally occurringsubstance created from the erosion of rock, the particle sizedistribution and sphericity vary considerably. A numerical difference of20 screen mesh standard may result in a particle size distributionbetween 10 to 30 for equestrian surfaces or between 20 to 40 for toathletic playing surfaces, for example.

In practice, the most inexpensive hard particulate material is usuallysand that is found in a naturally segregated deposit and/or has beenmechanically graded to suit various common construction uses, such asfor use in concrete mixes and roadbed construction. The demand for sandto be used for artificial grass installation is relatively low andtherefore if a design calls for a specially segregated or graded sandparticle size distribution, the cost of such material would be increasedsomewhat.

When deciding on the specific materials to be used in any location, itis preferable to use whatever acceptable sand is readily available nearto the. installation site. It is a relatively simple matter whenpurchasing resilient particles to specify the resilient particle sizedistribution such that it is within the ranges discussed above andsuperimposed on the measured sand particle size distribution. Resilientparticles must be processed, ground and shipped from a manufacturingfacility no matter where the installation site is located. The marginalcost of manufacturing resilient particles with a particle sizedistribution matching the particle size distribution of the sandparticles is relatively low compared to the alternative of grading thesize distribution of the sand particles to match the resilientparticles.

By manufacturing the resilient particles to match the size distributionof the readily available sand at the installation site, the bottom layerof infill with mixed sand and rubber particles of equally distributedsizes will result in the benefit of significantly reduced settling andseparation of the particle mixture in service.

In contrast, conventional mixes of resilient particles generally havesignificantly larger particles than the available graded sand. As aresult the lighter larger resilient particles migrate upwardly and theheavier smaller hard sand particles migrate downwardly under thecombined influence of gravity, vibration, rainfall and downwardlypercolating water. Segregation of differently sized particles leads toloss of optimum compaction and uneven traction in conventional mixedinfill layers.

It has been found by the inventor that the separation of hard andresilient particles in the mixed bottom layer can be prevented orsubstantially reduced by (1) selecting hard and resilient particles ofequal or substantially identical size distribution (2) selecting arelatively narrow range of particle sizes and (3) choosing generallyspherical particle shapes for both hard and resilient particles. Theminimal variation in particle size discourages compaction since thereare no relatively smaller particles to fill the interstices betweenlarger particles when all particles are of substantially equal size. Thespherical shapes reduce resistance to inter-particle displacement andreduce the tendency of adjacent particles to lock together.

The fibrillated grass-like synthetic ribbons at the top surface tend toretain the relatively large top rubber particles in a loose net-likeflexible structure. The loose criss-crossed net of fibrillated fibresalso allows dislodged rubber particles to work back into the underlyingtop rubber course when foot traffic passes over the particles andsynthetic ribbons. The combination of pure top rubber course and networkof fibrillated ribbons gives the look and feel of a natural turfsurface.

The synthetic ribbons between the fabric backing and the top courseprovide a degree of resistance to particle displacement in the mixedbottom course by forming an open net or lattice structure of verticallyoriented strands laterally cross-linked together. The mixed sand andrubber bottom course provides firm resilient support for the relativelythin rubber top course. The sand content of the mixed course inparticular provides the necessary weight for ballast and better drainagedue to the capillary action of the sand.

The relatively thin top course that is in immediate contact with theathlete's body, has a high resilience where physical contact occurs andresults in low skin abrasion due to the exclusive use of rubber. Thesand content in the mixed bottom course provides ballast weight to holdthe grass in place and to quickly drain the surface. Drainage isespecially necessary where there is a risk of freezing and selection ofa more coarse mixture for improved drainage may be required in coldclimates. The resilient particles in the mixed course also providesubsurface resiliency in addition to the top surface resiliency providedby the top layer.

The choice of hard and resilient particles of substantially equal sizedistribution substantially reduces compaction and reduces themaintenance requirements. The top pure rubber top course will alwaysremain substantially free of sand due to the choice of particle sizes.Sand may be displaced from the mixed bottom layer to the surface of thetop layer by agitation caused by contact with the player's cleats duringa game or practice session much in the same manner as conventional soilis disturbed by this action. However the size of sand particles ischosen to be smaller than the size of resilient particles in the topcourse. The downward washing of the displaced sand particles byrainwater draining through the top resilient surface or from thevibration and agitation of foot traffic returns the smaller sandparticles to the bottom course where they came from.

The two layer installation with rubber only in the top layer and mixedsand and rubber in the lower layer produces a resilient surface at lowercost and lower thickness than conventional methods such as described inU.S. Pat. No. 4,337,283 to Haas and U.S. Pat. No. 4,396,653 to Tomarin.The prior art infill layers with large and small particles tend tocompact or consolidate into a more firm compacted surface. The inventionmaintains its resilience even when used in thin layers since the toplayer is of pure rubber granules and the mixed lower course does nottend to separate or compact. Thus a more predictable long termresiliency is created.

The synthetic ribbons can be manufactured and tufted to the fabricbacking. It is preferred to slit the ribbons with relatively shortlongitudinal slits spaced apart across the width of the ribbons. Thenafter installation of the infill the upper portion of the syntheticribbons are fibrillated, split or frayed vertically on site by passingover the installed surface with a brush. The ribbons when manufacturedhave a longitudinally oriented structure and therefore aggressivebrushing action on the top surface tends to tear or split the ribbonsinto thinner grass-like strands by extending the slits longitudinally toform densely packed individual grass-like strands.

Where ribbons are brushed and split on site by brushing, the upperportions of the ribbons are frayed or split into thin grass-like strandswhereas the lower portions remain intact and are merely stretched openinto an expanded web, net or lattice structure, to a greater extent thanwhen the fibres were initially tufted into the backing. A direct benefitof this lattice structure is the stabilisation of the particulate infillby intermeshing the particles between the fibrillated grass-like strandsand within the expanded web-like fibre structure. The lower web-likeportion stabilises the infill and the upper grass-like portion allowsfor cleat penetration and release, rainfall penetration and drainage,adds a slight surface resilience due to the curved grass-like strands,and captures the large resilient particles of the top course in agrass-like net structure.

On-site fibrillation of the fibres also permits a more dense top surfacecoverage of grass-like strands. The relatively wide ribbons with shortslit perforations as initially installed can be spaced apart asufficient distance to permit granular infill to be installed betweenthe ribbons. When the infill has been fully installed, the brushing ofthe widely spaced ribbons splits them into thinner grass-like strandsthat fill in the gap between the ribbons and better cover the topsurface of the granular infill. The dense net of criss-crossedfibrillated strands contain the large top course rubber granules whileallowing cleat penetration and permitting water to drain through. Thesplit ribbons add better grass-like strand coverage of the visiblesurface at a lower cost. In applications not oriented to sports uses,such as in landscaping or decorative applications, less dense fibredistributions can be used resulting in lower cost for the same visuallyapparent coverage as conventional closely spaced synthetic grasses.

Further details of the invention and its advantages will be apparentfrom the detailed description and drawings included below.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be readily understood, one preferredembodiment of the invention will be described by way of example, withreference to the accompanying drawings wherein:

FIG. 1 is a cross-section through a synthetic grass assembly with infillinstalled showing the flexible sheet backing with upstanding ribbons andthe infill layer built up of a top course of relatively large resilientrubber granules and a bottom course of mixed hard sand and resilientrubber granules of identical smaller particle size distribution;

FIG. 2 is a similar cross-section showing the final configuration of thegrass-like strands slightly curved as a result of aggressive surfacebrushing to further fibrillate the ends of the ribbons;

FIG. 3 is a side view of a synthetic ribbon as manufactured with aseries of short longitudinally slit perforations;

FIG. 4 is a side view of a synthetic ribbon at the lower end twistedprior to tufting into the fabric backing and at the upper end laterallystretched to reveal the web-like grass-blade structure that resultingfrom the lateral stretching and longitudinal extension of the slits;

FIG. 5 is a table showing the graphical depiction of particle sizedistribution resulting from standard sieve analysis of infill courses;and

FIG. 6 is a table showing a visual representation of particles graded onthe Krumbein sphericity scale.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to FIG. 1, the invention relates to a synthetic grassassembly consisting of a pile fabric with an infill layer of particulatematter which is installed on a supporting soil substrate to provide agame playing surface.

The pile fabric includes a flexible sheet backing 1 that could includetwo or more layers of open weave fabric, one of which may bedimensionally stable netting to prevent stretching during installationand use. Extending upwardly from an upper surface of the backing 1 is alarge number of upstanding synthetic ribbons 2. As indicated in FIG. 1,the ribbons 2 are tufted through the backing 1 spaced apart in rows by adistance W and of a length L. The length ‘L’ of fibres is selecteddepending upon the total depth (5 plus 6) of infill and the desiredresilience of the completed synthetic grass assembly.

Disposed interstitially between the upstanding ribbons 2 upon the uppersurface of the backing 1 is an infill layer 3 of particulate matter. Theparticulate matter may be selected from any number of commonly availablehard granules such as: sand; hard aggregate; silica sand; gravel; slag;granulated plastic; and polymer beads. The resilient granules may beselected from: cryogenically ground rubber; rubber; cork; polymer beads;synthetic polymer foam; styrene; perlite; neoprene, ground tires, andEPDM rubber.

The infill layer 3 is made up of a top course 6 and a bottom mixedcourse 5. The mixed bottom course 5 is of intermixed hard sand granulesand resilient rubber granules. The mix is selected on the basisdistribution by volume of different sizes of hard granules and resilientgranules that are substantially identical and range in size between 0.5inches and 50 screen mesh standard. Preferably the range of particlesizes is limited to avoid small or fine particles that fill theinterstices between larger particles and encourage compacting. Thepreferred range is between 14 and 30 screen mesh standard. Depending onthe application, the range of particle sizes in the mixed course can belimited to between 10-30 , 15-30 or 20-40 screen mesh standard asselected to suit design parameters. The shape of hard and resilientgranules is substantially spherical and not angular as in the prior artto further discourage compaction and settling.

As shown in the graph of FIG. 5, a standard screen sieve analysis isdepicted with a vertical axis linear scale of “percent by weight passingthe sieve size” or alternatively “percent smaller” and the horizontalaxis being a logarithmic scale showing particle and/or sieve size. Theexample line shown in FIG. 5 indicate relatively uniform mixtures ofparticles with a narrow range of particle sizes. Ideally the line onFIG. 5 for sand particle size distribution and the line for rubberparticle size distribution are identical and would be shown superimposedon each other. However, as an example, the 10-30 range mentioned aboveis graphically illustrated as a shaded zone within which any line willmeet the requirements of this particle size restriction.

The top course 6 is substantially exclusively of resilient rubbergranules. An upper portion 7 of the synthetic ribbons 2 extends upwardlyfrom a top surface 8 of the top course 6. The resulting artificial grasssurface can be adapted for several indoor and outdoor uses, such as:athletic playing fields; horse racing fields, playgrounds, landscapedareas, and recreational areas.

In order to deposit dual layers, brushes pass over the backing with amixed sand and rubber material many times to ensure that the ribbons areupstanding when embedded in the infill and not submerged under theinfill, and to further slightly expand the ribbons to open the slits andproduce a lattice structure that stabilizes the infill preventingexcessive displacement of the infill particles after installation. Afterthe mixed lower infill layer is laid a substantially pure rubberparticulate material is placed as a resilient top layer.

To deposit the bottom layer a spreader may be used and thereafter thesurface is brushed to raise the nap of the pile fabric and position theribbons 2 in a generally upright position prior to depositing the topcourse 6. After spreading each layer, it is necessary to brush thesurface and raise the ribbons to an upstanding position as shown in thedrawings.

It may be preferred that after installation of the top course 6, theupper portion 7 of the synthetic ribbons 2 is further fibrillated byaggressively passing over the surface with a brush. This operationsplits the upper portions 7 and spreads the strands uniformly over thetop surface 8. The manufactured width of the ribbons 2 is relativelywide such as one inch and the on-site brushing operation. further splitsthe ribbons opening the slits longitudinally and forming thinnergrass-like strands of a thinner width as illustrated. The upper ends ofthe ribbons 2 are brushed more vigorously to achieve the followingadvantages over prior art methods. Laying over of the fibrillated upperportions 7, interlocks the ribbon ends into a loose network which morerealistically simulates the appearance of natural grass. The fibrillatedends impart a slight resilience since they are slightly raised orfluffed and more accurately simulate the resilience of natural grasswhen balls, during play, bounce on the completed surface. The bent overends as well hide the rubber crumbs of the top course 6 from view, holdthe crumb particles in place and allow a movement of dislodged crumbsback and forth between the top course 6 and upper side of thefibrillated ribbons 2. By splitting or fibrillating the ends of theribbons 2, less surface tension is created and water more easilypermeates through the top surface 8 and is drained away through thebottom course 5.

The ribbons 2 include a top structure of multiple grass-like strandsfibrillated on site and an expanded web-like lower structure leftsubstantially in their original state but mechanically expanded into aweb lattice due to interaction with the infill as it is deposited.Ribbons may be chosen from fibers such as polypropylene, polyethylene,nylon and plastic. A mix of thick and thin width of fibrillated strandsproduces a more natural appearance and causes a ball to roll in a morepredictable manner depending on the resistance of the fibers to the ballduring play. Modification of the ribbon width and density in the grasswill also modify the ball rolling characteristics.

The ribbons, when initially tufted to the fabric backing, may be of awidth in the range of 1-3 inches, and when fibrillated the individualgrass-like strands may be in the range of 1 mm to 15 mm (⅛ inch to ½inch approx.) in width. Expressed in terms used in the art, the strandsrange from 800 to 5000 Denier, and the thickness of ribbons and strandsrange preferably from 45 to 200 microns (μ).

It has been found through experiment and experience that the size andshape of hard granules and resilient granules significantly affects theturf performance characteristics. It has also been found that thespacing of ribbons and the variation in depth of infill can have stronginfluence on the performance of the synthetic grass assembly.

The hard and resilient particle sizes should range between 0.5 inchesand 50 U.S. screen mesh standard, however preferably a narrower range of14-30 avoids the risk of compaction. Hard granules larger than 14 screenmesh standard can be perceived as somewhat abrasive by users of theathletic surface if direct contact is made. However, since the fibresabove the top surface tend to arch over and shield the user from directcontact with an arched resilient fibrous matting of synthetic fibers,somewhat larger particles can be used without perceiving the particlesas abrasive. Particles smaller than 50 screen mesh standard will tend toimpede the percolation of water and detrimentally affect the drainagecharacteristics of the infill layer 3 in relatively wet climates. In dryclimates, use of smaller particles may be desirable to maintain anoptimal moisture content for optimal level of compaction and resilience.Larger resilient particles (such as 14 screen mesh standard) may be usedwhere skin contact with the surface and potential abrasion from thenature of the sport are expected. Preferably the sand is washed andgraded to remove substantially all the fine particles below size 50mesh.

The natural tendency of the large relatively light rubber particles tomigrate to the top and the complementary tendency of smaller heaviersand particles to migrate to the bottom of the infill layer 3 is reducedby use of equally sized particles. Particle migration is also reduced bythe interaction with the synthetic web-like ribbon structure and by theuse of spherical particle shape. The bottom course of the infill retainsits initial mixture of equally sized sand and resilient particles due tothe selection of substantially identical particle sizes and theinterference to particle movement resulting from the web-like structureof the ribbons in contact with the bottom infill layer. Thesecharacteristics of the infill tend to discourage compaction and maintainthe uniform predictable resilience of the infill.

With a pure rubber resilient top course 6, resilience is provided at thecontact surface where the perception of resilience actually needed.Preferably the particle size of rubber particles in the top layer 6 ofinfill are larger than the sand and resilient particles in the bottomlayer 5. The larger particles of the top layer permit smaller particlesof the bottom layer to fall back down through gaps between the largeparticles, and as a result, the particle size compositions of the layersremain distinct. The resilience of the final layer of infill can be finetuned by testing resilience at the surface and gradually spreadingrubber particles to marginally increase the thickness of the top course6 and achieve the desired resilience of the final top course.

The synthetic ribbons are preferably disposed in rows spaced apart aselected minimum distance “W”. Depending on the firmness desired and thedegree of freedom required for cleats to rotate for various sports, thespacing “W” can vary between 2.25 inches and 0.625 inches or less. Acloser spacing provides firmer support for the infill 3 whereas a widerspacing permits easier rotation of embedded cleats.

The depth of the infill layer 3 relative to the length “L” of syntheticribbons can range from 90% to 40% however the preferred range for mostapplications will be 85% to 55% or 80% to 70%. For example, where thelength of ribbons L is 2 inches, a depth of infill equal to 75% would bea depth of 1.5 inches (2.0×0.75=1.5) with the remaining 0.5 inches ofribbon extending above the top surface of the infill.

Although the above description and accompanying drawings relate to aspecific preferred embodiment as presently contemplated by the inventor,it will be understood that the invention in its broad aspect includesmechanical and functional equivalents of the elements described andillustrated.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A synthetic grassassembly for installation on a supporting substrate, the assemblycomprising: a pile fabric with a flexible sheet backing and a pluralityof upstanding synthetic ribbons of a selected length, the ribbonsextending upwardly from an upper surface of the backing; an infill layerof particulate material disposed interstitially between the upstandingribbons upon the upper surface of the backing and of a depth less thanthe length of the ribbons, the particulate material selected from thegroup consisting of hard and resilient granules, wherein the infilllayer comprises: a bottom course of intermixed hard and resilientgranules of substantially identical size distribution, disposed upon thetop surface of the backing; and a top course substantially exclusivelyof resilient granules disposed upon the bottom course, an upper portionof the synthetic ribbons extending upwardly from a top surface of thetop course.
 2. The synthetic grass assembly according to claim 1,wherein the resilient granules in the top course are larger than theresilient granules in the bottom course.
 3. The synthetic grass assemblyaccording to claim 1, wherein the hard granules and resilient granulesin the bottom course are of a shape defined in the range of 0.5 to 0.99on the Krumbein scale of sphericity.
 4. The synthetic grass assemblyaccording to claim 3, wherein the hard granules and resilient granulesin the bottom course are in the range of 0.6 to 0.9 Krumbein scale. 5.The synthetic grass assembly according to claim 1, wherein the resilientgranules are selected from the group consisting of cryogenically groundrubber, rubber, cork, polymer beads, synthetic polymer foam, styrene,pertite, neoprene, and EPDM rubber.
 6. The synthetic grass assemblyaccording to claim 1, wherein the hard granules are selected from thegroup consisting of sand, hard aggregate, silica sand, gravel, slag,granulated plastic, and polymer beads.
 7. The synthetic grass assemblyaccording to claim 5, wherein the hard granules are selected from thegroup consisting of sand, hard aggregate, silica sand, gravel, slag,granulated plastic, and polymer beads.
 8. The synthetic grass assemblyaccording to claim 1, wherein the particulate material of the infillcomprises granules of size ranging between 0.5 inches maximum nominaldiameter and 50 screen mesh standard.
 9. The synthetic grass assemblyaccording to claim 8, wherein the particle sizes of 80% by weight ofhard granules and resilient granules in the bottom course aredistributed in a range spanning a numerical difference of 40 in screenmesh standard.
 10. The synthetic grass assembly according to claim 9,wherein the particle sizes of 80% by weight of hard granules andresilient granules in the bottom course are distributed in a rangespanning a numerical difference of 20 in screen mesh standard.
 11. Thesynthetic grass assembly according to claim 1, wherein the syntheticribbons are disposed in rows spaced apart a selected minimum distance.12. The synthetic grass assembly according to claim 11, wherein themaximum distance between rows of synthetic ribbons tufted in the fabricbacking is 2.25 inches.
 13. The synthetic grass assembly according toclaim 12, wherein the maximum distance between rows of synthetic ribbonstufted in the fabric backing is 1.0 inch.
 14. The synthetic grassassembly according to claim 13, wherein the maximum distance betweenrows of synthetic ribbons tufted in the fabric backing is 0.625 inches.15. The synthetic grass assembly according to claim 1, wherein depth ofthe infill layer is in the range between 90% to 40% of the length ofsynthetic ribbons.
 16. The synthetic grass assembly according to claim15, wherein depth of the infill layer is in the range between 85% to 55%of the length of synthetic ribbons.
 17. The synthetic grass assemblyaccording to claim 16, wherein depth of the infill layer is in the rangebetween 80% to 70% of the length of synthetic ribbons.
 18. The syntheticgrass assembly according to claim 1, wherein the synthetic ribbons arefibers selected from the group consisting of polypropylene,polyethylene, nylon, and plastic.
 19. The synthetic grass assemblyaccording to claim 2, wherein the upper portion of the synthetic ribbonsare fibrillated into individual strands of a width in the range between1.0 to 5.0 mm.
 20. The synthetic grass assembly according to claim 1,wherein the synthetic ribbons are of a thickness in the range between 45to 200 microns.